Recovery of acetaldehyde from gaseous mixtures containing the same



june 8, 948 v K. H. w. TUERCK ET A1. 2,442,942

RECOVERY OF ACETALDEHYDE FROM GASEOUS MIXTURES CONTAINING THE SAME FiledJan. '7, 1943 AcT/c Acln oLuTloN OF CA TALysT Coo/ 5R By 2%. Www/Patented June 8, 1948 l nous ivux'roitss coN'rAiurNs'rnEslimKrruemrehjwaiter'ruerckgausteaiigaianue Alipiieatimsanuary 7, 1943,-serial No. 471,612 1.1i Great Britain Septlfmllll @49451 f.; sectionf1f, Pub-netsw 69o,-2ugust c; 1946 Patent expires September l11, 1961iff if HW" .Thisinventionis lorimprovementsin crfrelating-to `therecoveryof acetaldehydef-rom. gaseous mixtures: andi :has for' anobjectl to, overcome the cliiiiculties whicharegexperienoedintherecovery ofzaceta-ldehyde owing to its low boiling point and highvolatility.

`En zcases where-.acetaldehyde vapourY -hasf to be recovered fromgaseous'mixtures by absorption, asfforgexampleiinfthe hydrationof acetylene,the dehydrogenatiom of alcoholr orfthe oxidationv Aof acetaldehyde to`acetic acid- (and/or..acetic anhydride), the use oflargefscrubbingfunits and large amounts otscrubbing liquidf which isnecessary in .uiew ofl thehighvapounpressure.of acetaldehyde-,yinvolvesaconsiderableloss of acetaldehyde duringlthe. recovery, apartfroin .thedisadvantagesof handling and, distilling large amounts .of scrubbingliquids. Organic. solvents offer the ad'- vantage sof `recovering.. thealdehyde in'l'a niore or less. waterefreemedium, but as scrubbingliquids they are less eicient'than water, in which ace'tal dehydeexertsarelatively small vapor pressure at low concentrations. Y

It is 'an object of the present .invention "to'iue creasethe eciency oforganic scrubbing liquids for acetalde'hyde vand. to increase" the"coutent1 of aldehyde'in the scrubbing liquid leaving thescrubbingsystem. According tothe present'invention` 'a process for`the`Y recovery i of acetafldehyd'e 'from gaseous mixturescontaining itcomprisesfbringing' the said gaseous mixture into contactv with aniriert organic liquid which is a. solventforlacetaldehyde and-'forparaldehydefin all proportions-, and'fwhich contains-'anacidicpolymeri-sing agentrcapable of converting vthe'a'cet21.lde'hyiief yto lparald'eh-yde.' y-It will-be appreciatedfthatowing to'thevery muchhigher'boiling point of'paraldehyd'e as compared with 'acetaldehydeirandi the? loWer'-voatility lof paraldehyde as comparediwithacetaldehyde; the size ofthe; scrubbing uniti can befversmnuch reducedin comparison with the conventionalscrubbingeunits inwhichfacetaldehydef-is znefrelyrdise solvedzin rthe` scrubbing liquid`andi'furthermore that "the amount -.of;th'e scrubbing -'1iquid' tcan be'much reduced.; 'As inertrsoivents we include those organic substanceswhich do noti-react' with acetaldehyde under ltherconditicms of theabsorption,y Whichcdoinotneutraiise"the polyrnerisation'Icata-` lyst:and Whichdo notresinify in the presence of the small amountsofcatalystused. ff' i iA-cetic vacidraznd paraldehyd'e are specially`suitable for-this purpose. At small aldeh-yde coneen`r tratioirs;ysolvents: of. low- -molecnlan weight-` influe; ence the equilibriumratio between acetaldehyde 9 Claims. (Cl. *260-340) i and paraldehyde inavour-'ofaceta1dehyde- -lll'e therefore-. prefer to 'uselsolvents of aA"mclecular weight higher ltliauvil; 'especiallyi-thef gases tobewas-hed contaiirreljatlvel-y-smal1axnotmtsfer gg, les'sfthan' 2001g.facetaldehydsa/1111*="4 Ghlorinated hydrocarbons-l suchas carbon'tetrachloride v1and trichlorethylene are suitable solvents fqr'thispurpose. Substances which are suitable fas" acidicpclymerizingcatalysts-are strong acidssuch-es sulphuric acid;-phosphoricecidgorgauicsulphonie acids-suchas pto1uenesulphonic acid andacidic salts suchaszinc chgorlfle.'.-=v f v :It:has-alreadybeenfpfoposedfin prioreritish Patent Nol. 132,5 29to passasasecus mixture containing acetaldehydeyover aqueoussulphuric acidwhereby the acetaldehyde was'converted into parialdeh'ydewhichfoatsionfthe surcerofth'e aduce' ous" sulphuric-'lacid solution?2-II'he Ybroc'ess, how. ever; producesF-say heterogeneous"frnixturefiiroin which the rparaliieiiyde has'tcL be freovedbydecantatfonipioeesseswhereas theiprocessoffthepresentfiuveutionfpriducesfaz homogeneoussolutinoffparalehyde'inithesohrentuseii" lil Y*Moifoverwef-hayeffuiidfthat tli'rt ci li'- merisatintifsattalt!hydtiaiialdlfiyd ccordi-ng '1to1 theJ restlfinvntiii is'iiaiiyl times greaterithan that btaindby the-use-bf aqueous solutions*of slphuric'j'id and thelate iii-th latter process is so slow vas to belci no technical Value. z Y- es.: :Y: :..2 1f.' i2. :i12-.ijf il.' Forexample, We have lfound that if "aceta'ld 'ev hyd'ef isy 'dissolved toL"forni 'ila 3528.75" solution by weight-in ca) ornaments sulpuurieaciuui'yg 10% "aqueous;s "ulphuric` 'jcid, or acetic "acid containingbfi-vifuuuhuricV sont the; amount f acetal'dehyde'"polyrnerisei tpaaldehyd Vis) nu in 3o minutes-', fndsm iii 32 hoursrfb) s175111 3'0minutes and 58% in 24 hours, (.c) 80% in the A feature of thei'm'zen't'ion' consists `iri`thtftl`ie amount` of. the .acidicpolymerislng agent usedjn thesolvent isof thefrderfi byweght o less;

an amount of as little as OL'1 by' w'elght'or everi lesscan successfullybe usedwhilstwh'ere Ai'gffesaid polymerising agent is a stro'ug'inorganic acid the amountA thereof is preferably. always" less Vthan0.5% 4 by weight.- If acetic acdfis 'usadas v.the solvent, e..g-.,iii-.quantities of-niore .than 5,0%', 0.011% orievenless of theabovementioned catalysts are suicient.. Y lf-l- 1, In view of` the factthatitgis-known that strong acids are not onlystrongpolyineifisingcatalysts but elsostrong-cendensatieh.catches-meestal dehyde, it is surprising that underthe conditions of the process according to the invention the solutionsobtained are practically freefrom condensation products of acetaldehyde.

The process of the present invention is of very wide application incommerce. For' example, the process may be applied to the recovery ofacetaldehyde vapours from `processes in which acetaldehyde is oxidisedto form acetic acid with or without acetic anhydride, whilst it may alsobe utilised |for the preparation 'of pure acetaldehyde vapours since theparaldehyde can be puried and then depolymerised to produce pureacetaldehyde vapours.

It is an advantage of the process -of vthe linvention that it providesscrubbing liquids which have little or no corrosive action upon theusual materials of plant construction, e. g., aluminium. The smallamounts of acidic catalysts which are necessary in accordance with theinvention do not substantially corrode the plant, whereas aqueoussolutions of such catalysts on the other hand exert a pronouncedcorrosive action on the plant. The absorption may be carried out in theusualv scrubbing units. We prefer to use a scrubbing'device whichenables the gas and the liquid to flow in counter-current to each other.i

In order to obtain the'maximum eiiiciency it is advisable to employ atime of contact between gas and liquid sufficient to polymerize most ofthe acetaldehyde in the gas mixture under treatment. Generally speaking,from 30 to 60 seconds contact has been found to be satisfactory.

A preferred method of carrying out the invention is to recycle thescrubbing liquid. Thus, for example, `the liquid running off at thebottom ofthe scrubbing tower is collected in a tank, in order to allowsuicient time for completing the'polymerisation of the absorbedacetaldehyde, andthe lliquid is thenpartly'returned to the scrubbingcolumn at a suitable point preferably slightly above the'centre of thecolumn, while fresh solvent with or`withoutia polymerising catalyst isintroduced at the top of the column.

Sutable'temperatures for the absorption are 525 C.; we prefer tocarryout the absorption at 15-20 C. The temperature may be regulated bycooling the scrubbing towers indirectly or, if the quantity ofyscrubbing liquid is suiiicient, by cooling the latter before it entersthe scrubbing tower. Y l

vThe process ofthe yinvention is particularly suitable for useinconjunction with acetaldehyde oxidations. These oxidation processesgenerally utilise a-g'aseousfmixture of acetaldevhyde vapour in anoxygen-containing gas which gaseous mixturelispassed into acetic acidcontained in the reaction vessel and maintained at a temperature from 40to 100 C. whereby a porion of the acetaldehyde is oxidised to acetic aciThe unoxidised portion of the acetaldehyde feed is recovered by theprocess of the invention to yield a solution of paraldehyde in a solventwhich also contains a small amount of the polymerising agent.

As the polymerisation of acetaldehyde to paraldehyde is aireversiblereaction, it will readily be understood that the paraldehyde solvent ifmaintained at a low temperature, of the order of 20 C., will absorbacetaldehyde and convertV it to paraldehyde which at thattemperatureremains dissolved in the solvent.

The solution whenheated will evolve acetaldehydevapour as the-higher'temperature favours 4 the reverse reaction, namely the depolymerisationof paraldehyde to acetaldehyde.

Thus it will be appreciated that the scrubbing liquor from the scrubbingunit can be passed to a Vessel in which it is heated to evolve acetalde-Vhyde vapours which vapours can be admixed with the fresh feed ofacetaldehyde to the reaction vessel. Acetic acid is a convenient solventwhich may be used and this is advantageous also since the scrubbingliquor may be a part of the reaction liquid in the reaction vessel whichis Withdrawn from the reaction vessel, cooled and passed to thescrubbing unit from which it is recirculated back to the reactionvessel. It is also possible to carry out the process by returning thescrubbing liquid issuing from the scrubbing column directly to the topof the scrubbing column for treating a further quantity of acetaldehydecontaining gas. This is due to the fact that it has been found that theefficiency of the scrubbing liquid is maintained over long periods ofuse so that it does not require to be renewed frequently as is the casewith conventional scrubbing solvents.

The above mentioned procedures are particularly adaptable for processesfor the production of acetic acid or acetic anhydride utilisingparaldehyde as the source of acetaldehyde. In such a. processparaldehyde may Ibe fed into the reaction vessel in admixture with asmall quantity of a depolymerising agent and an oxygencontaining gas isthen introduced into the reaction vessel whereby oxidation is caused.

Alternatively, in any of the foregoing processes the acetaldehydevapours can be recovered in the scrubbing unit in the form ofparaldehyde in a solvent, which is circulated in a closed circuit asbetween the scrubbing unit and an acetaldehyde regenerating unit, andwhich does not enter the reaction vessel. Thus it is possible to avoidany corrosion of the reaction vessel which might be caused by contact ofthe acidic polymerising or depolymerising agentswith the material of thereaction vessel at the elevated temperature of reaction.

The scrubbing solutions which are obtained according to the process ofthe invention contain paraldehyde together With small amounts ofacetaldehyde. If paraldehyde is used as the solvent, the scrubbingproduct is paraldehyde con-` taining only acetaldehyde and the acidicpolymerising agent. By distilling, pure acetaldehyde can be easilyobtained.

By neutralising the polymerisation catalyst in the usual way, e. g.,with salts of fatty acids, the solutions can be worked up forparaldehyde.

The solutions themselves are convenient means of storing the recoveredacetaldehyde, which otherwise has to be kept under pressure or inspecially cooled tanks.

It is, however, a special feature of our invention to use the solutionsobtained according to our process as raw material in operations whereacetaldehyde is reacted in an essentially water-free phase, e. g., inthe manufacture of acetic acid and/or acetic anhydride by reactingacetaldehyde in the liquid phase with gaseous oxygen. The solutions,especially those which contain only paraldehyde and no other solvent,can conveniently be used to produce gaseous mixtures containingacetaldehyde, e. g., acetaldehyde-air mixtures for the production ofacetic acid, by passing a current of air through the solutions at agiven temperature at which the solution develops the desiredacetaldehyde vapour pressure, Vand -leading the resulting `gas-mixtureinto the oxidation vessel.

The following examples 'illustrate the manner in which the Ainventionmaybe `carriedinto eiect:

AEntf/imple 1.-'Ilie reaction gases obtained from the 'catalyticldehydrogenation of ethanol, after having passed through a condenserwhich 'removes the unchanged ethanol, and containing 600 g.acet'a`ldehyde/m-3, are introduced Iinto `a packed column, height 3m.,diameter 17.5 cm., ata rate of 3:3 m.3/hr., where they are 'scrubbed by4.9 rkg. acetic acid Vper hr. containing 0.2% by weight of 'sulphuricacid. The Ltemperature in the column is keptat 16 Ckby externalcooling,the contact time being 53 sec. for the liquid. More than 97% by weightvof the aldehyde in the gas is recovered. bBy using acetic Aacid aloneonly 65% -by weight of the acetaldeh-yde vcould be recovered under thesame conditions.

Example 2.-In 'a vessel which -is Yprovided with a stirrer and whichcontains a Isolution of acetaldehyde and 0.2% by weight of sulphuricacid in acetic acid, air is introduced while the temperature -ismaintained at li-100" C. At

the ysame time the amount of acetaldehyde which is either oxidized,carried awayby the waste gases or withdrawn together with the acid, isbeing replaced continuously. VPart of the reaction liquid iscontinuously withdrawn from the reaction vessel and cooled down to about250l C., so that the free acetaldehyde is polymerized to paraldehyde,and then 4fed into thewtop or a packed column, so that it ows incounter-current to the gases coming from the oxidation yessel, down tothe said vessel. If 4the concentration of the acetaldehyde inthereaction liquid is kept at or below 10% by weight, l m5* of the wastegases at the top of the 'reflux column 'carries away 60 g,acetaldehyde/m-3; whereas without the use of the polymerisation catalystin the circulating solution, the gas carries away 390 g.acetaldehyde/m-3, i. e., a reduction of the' losses t0 1/5. With a 30%Weight solution of the aldehyde the corresponding figures are 110g./`r'n.3 and 700 g./m.3.

In this Way the concentration 'of Vfree acetal'dehyde is at a minimum atthe top of the scrubbing column, where the elliuent gases meet theincorning cold circulated solution. Of course, the e'iect can beimproved by variations in the rate fof flow of the circulating solutionand by additional cooling of the scrubber s that greater parts of thecolumn are kept at a low temperature while the solution has enough timevfor the polymerisation of the acetald'ehyde before it enters the top ofthe reaction' vessel. i

The surprising and unexpected elect of the new process is that, underthe conditions nientoned in Example 2, the yieldsin acetic acid areexcellent, though the inorganicl acids are' known as active condensationcatalysts for acetaldehyde. y

The oxidation of` acetaldehyde can carried out with or without thepresence' of special oxidation catalysts. It is essential, however, thatthe oxidation catalyst does not neutralize the activity of thedepolymerising agent. Thus, lad.-V vantageously, acidic or non-alkalineoxidation catalysts such as vanadic acid and metal salts of strong acidsor complex acids can be used together with the strong acids abovementioned. Another catalyst, which makes it possible to `use onlymoderate temperatures in the oxidation vessel, is manganic acid.

A modification of the process of Example 2 is the addition `of theoxidation.catalyst andof the polymerisatio'n catalyst at Vdifferentstages.Y Thus ltheV oxidation catalyst, afg., manganese acetate orAcopper 'acetate 'is added to the reaction ves'sel, whereas thedepolymerising acid is `addedimmediately before or after the solution vis'cooled. Thus it is possible to maintain in `the 4hotreaction vessel'a minimal concentration of the depolymerising; acid, land at thejsamctime to effect 'a suincient polymerisation Vin lthe cool part of thecirculating liquid (making use of the depolymerising effect Vof the hightemperature). A A,

The reaction vessel mentioned 'above can, of course, be replaced by a)reaction tower, which may be packed or so designed that an interactionbetweenthe oxidizeinggasand the .liquid is easily possible, Such anoxidising tower may contain an4 upper part., used `as a scrubbingcolumn, whichumay be provided with means Vfor indirect cooling. i:Insteadv or the -c iirculating solution, a cooled solution of thepolymerising agent in .acetic acid may be sprayed into the scrubbingcolumn.

It is also possible to reed the scrubbing column with paraldehydeorrwithparaldehyde and acetic acid or with paraldehyde `and another circulatingsolution, the amounty of paraldehyde being preferably -such as toreplace the amount of acetaldehyde oxidised and withdrawnrfrom thesystem. Such an arrangement is especially suitable in cases where aceticanhydride is to be produced by ldirect oxidation, an excess ofparaldehyde acting as diluent.

In order to obtain the acetic, acid from the reaction mixture, thelatter is distilled so` that acetaldeyde is removed as 1 ow boilingfraction. Or the reaction liquid may be distilled after thedep'olymerising acid has been neutralised, e. g. by sodium acetate. Inthis case, an azeotropic mixture consisting of equal parts of aceticacid and paraldehyde can be withdrawn as head fraction and returned tothe oxidation, while, as a second fraction, pure acetic acid isobtained. If the reaction mixture contains any water, this ca'nberemoved during the distillation as an azeotropic mixture withparaldehyde at 89 C. /760 mm. Hg, so that the resulting acetic acid isobtained water-free without resorting to a costly fractionation. We havealso found that it is possible to obtain acetaldehyde alone from areaction mixture in which the acidic depolymerising agent has beenneutralised, if the distillation is conducted at a high reflux ratio, sothat the greater time of contact `between acetic acid and paraldehyde atthe temperature in the distillation vessel yis, -such as totalisev a,slow depolymerisation of the paraldehyde, even in the absence of astronger acidic dpolyrnerising agent.

The followingvdescription is of an alternative methodl of carrying'rou'tthe above processV in which the liquid solution containing paraldehydeobtained vby1 washing out acetaldehyde vapour with the paraldehydesolvent containing the polynierising agent is distilled, after thepolymerising agent Yhasbeen neutralised, so as to isolate theparaldehyde in the usual manner, The paraldehyde thus isolated can thenbe returned to the reaction vessel together with a small amount of adepolym'erising agent.

Paraldehyde :can also be used instead of acetaldehyde for themanufacture of acetic acid in the Afollowing manner: Q

Paraldehyde, which is maintained at al temperature of about 310 C. andwhich contains a small amount of depolymerising agent has a stream ofair passed through it so that the air carries away the evolvedacetaldehyde vapour, the gaseous stream being led into an oxidationvessel Where it is oxidised in the usual way with or without theaddition of a depolymerising catalyst. The advantage of the use ofparaldehyde instead of acetaldehyde in the vaporiser is, inter alia,that the saturation of the feed vapours can be more conveniently andaccurately controlled. Preferably the air stream, after being passedthrough the paraldehyde, is led through a reflux condenser so thattraces of paraldehyde carried over in the air stream may be returned tothe saturator.

Alternatively, it is possible to pass the oxygencontaining gas throughthe solution recovered from the scrubbing unit, the solution beingmaintained at a suitable temperature so that acetaldehyde is regeneratedand carried back with the stream of oxygen-containing gas into theoxidising vessel. In this process any diiculty arising from contact of astrongly acidic polymerising or depolymerising catalyst with thematerial of the oxidising vessel is avoided.

It will be appreciated that although the process for the recovery ofacetaldehyde has been described as applied to oxidation processes, itmay also be applied to any process in which it is required to recoveracetaldehyde.

What we claim is:

1. A process for scrubbing acetaldehyde from a gaseous mixturecontaining it in admixture with at least one normally gaseous substancewhich comprises bringing the said gaseous mixture into intimate contactwith acetic acid which contains in solution therein up to one-half ofone per cent of an acidic polymerizing agent selected from the groupconsisting of sulphuric, phosphoric, and p-toluene sulphonio acids,capable of converting the acetaldehyde to paraldehyde, by passing thesaid gaseous mixture and acetic acid solution in countercurrent flow toeach other, while maintaining the said solution at a temperature of to15 C., whereby absorption and polymerisation of the acetaldehyde takeplace.

2. A process for the removal of acetaldehyde from a gaseous mixturecontaining it in admixture with at least one normally gaseous substancewhich comprises introducing said gaseous mixture in countercurrent flowinto an acetic acid solution of an acidic polymerising agent selectedfrom the group consisting of sulphuric, phosphoric, and p-toluenesulphonic acids, said polymerising agent being present in an amount notexceeding 0.5% by weight of said acetic acid solution, maintaining saidsolution at a temperature of between 5 C. and 25 C. and recovering theparaldehde-contalining solution.

3. A process for the removal of acetaldehyde from a gaseous mixturecontaining it in admixture with at least one normally gaseous substancewhich comprises introducing said gaseous mixture in countercurrent lowinto an anhydrous acetic acid solution of an acidic polymerising agentselected from the group consisting of sulphuric, phosphoric, andp-toluene sulphonic acids, said polymerising agent being present in anamount not exceeding 0.5% by weight of said anhydrous acetic acidsolution, maintaining said solution at a temperature of between 5 C. and25 C. and recovering the paraldehyde-containing solution.

4. A process for the recovery of acetaldehyde from a gaseous mixturecontaining it in admixture with at least one normally gaseous substancewhich comprises introducing said gaseous mixture in countercurrent flowinto an acetic acid solution of an acidic polymerising agent selectedfrom the group consisting of sulphuric, phosphoric, and p-toluenesulphonic acids, said polymerising agent being present in an amount notexceeding 0.5% by weight of said acetic acid solution, maintaining saidsolution at a temperature of between 5 C. and 25 C., recovering theparaldehyde-containing solution thus produced, subjecting it todistillation to regenerate pure acetaldehyde and recovering said pureacetaldehyde as distillate.

5. A process for the removal of acetaldehyde from a gaseous mixturecontaining it in admixture with at least one normally gaseous substancewhich comprises introducing said gaseous mixture in countercurrent ilow,with a contact time of from 30 to 60 seconds, into an anhydrous aceticacid solution'of an acidic polymerising agent selected from the groupconsisting of sulphuric, phosphoric, and p-toluene sulphonic acids, saidpolymerising agent being present in an amount not exceeding 0.5% byweight of said anhydrous acetic acid solution, maintaining said solutionat a temperature of between 5 C. and 25 C. and recovering theparaldehyde-containing solution.

6. A process for the removal of acetaldehyde from a gaseous mixturecontaining it in admixture with at least one normally gaseous substancewhich compri-ses introducing said gaseous mixture in countercurrent flowinto an anhydrous acetic acid solution of sulphuric acid, theconcentration of said sulphuric acid in said acetic acid being from0.01% to 0.2% by weight thereof, maintaining said solution at atemperature of between 5 and 25 C. and recovering theparaldehyde-containing solution.

7. A process for the removal of acetaldehyde from a gaseous mixturecontaining it in admixture with at least one normally gaseous substancewhich comprises introducing said gaseous mixture in countercurrent flowinto an anhydrous acetic acid solution of phospheric acid, theconcentration of said phospheric acid in said acetic acid being from0.01% to 0.2% by weight thereof, maintaining said solution at atemperature of between 5 and 25 C. and recovering theparaldehyde-containing solution.

8. A process for the removal of acetaldehyde from a gaseous mixturecontaining it in admixture with at least one normally gaseous substancewhich comprises introducing said gaseous mixture in countercurrent flowinto an acetic acid solution of an acidic polymerising agent selectedfrom the group consisting of sulphuric, phosphoric, and p-toluenesulphonic acids, said polymerising agent being present in an amount notexceeding 0.5% by weight of said acetic acid solution, maintaining saidsolution at a temperature of between 15 C. and 20 C. and recovering theparaldehyde-containing solution.

9. A process for removing acetaldehyde vapours from a gaseous mixturethereof with at least one normally gaseous substance and recovering itin a form from which it may be regenerated as acetaldehyde whichcomprises passing said gaseous mixture in countercurrent flow and inintimate contact with an organic solvent for acetaldehyde andparaldehyde which is inert toward-s said substances, said solvent beingselected from the group consisting of acetic acid,

KARL HEINRICH WALTER TUERCK. ERI-C HARVEY BRITTAIN.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 1,300,451 Morton Apr. 15, 19191,306,963 Koetschet et al. June 17, 1919 Number Number Name DateBackhaus et al Dec. 13, 1921 Herman et al Sept. 14, 1926 Sator July 17,1928 Hermann et a1 June 24, 1930 Muchler Conradi et al. Mar. 20, 1934Fuchs Apr. 24, 1934 Johnson et al Mar. 19, 1935 Dreyfus Jan. 19, 1937Frank Dec. 8, 1942 'I'hompson May 4, 1943 Vogel Aug. 24, 1943 FOREIGNPATENTS Country Date Great Britain May 24, 1923 OTHER REFERENCES 2oKamer-Organic Chemistry (1938), Nordeman Pub. Co., N. Y., page 149.

